Example usage:

Rationale:

The RGB additive colour model is commonly used for defining colours: the HTML
hexadecimal notation for colours (such as #9263AA) simply consists of three hexadecimal
values placed together. This macro allows you to create such colours computationally,
by providing variables for certain components.

Details:

This macro takes the same range of numbers as the CSSrgb() function.

Giving values higher than 255 or lower than 0, or with a fractional part,
will cause an error.